Update dependencies and migrate to Gradle 9 / Dokka v2

Dependency bumps: Kotlin 2.3.20->2.3.21, Coroutines 1.10.2->1.11.0,
Ktor 3.4.2->3.5.1, KSP 2.3.6->2.3.9, MicroUtils 0.29.2->0.30.0,
Dokka 2.0.0->2.2.0, Versions plugin 0.53.0->0.54.0, NMCP 1.4.4->1.6.0.

Gradle wrapper 8.13->9.6.1 with build-script fixes for Gradle 9:
Project.exec() -> providers.exec(), tasks.whenTaskAdded -> tasks.configureEach.

Dokka migrated to the Dokka Gradle Plugin v2. The docs module is now
included as the KDocs aggregator (dokka {} DSL with sourceRoots, new URI,
ProcessIsolation heap for the generator worker), excluded from binary
compatibility validation, and the kdocs workflow runs :docs:dokkaGenerate.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/kdocs.yml

@@ -12,10 +12,10 @@ jobs:
         with:
           java-version: 17
       - name: Build
-        run: ./gradlew dokkaHtmlMultiModule
+        run: ./gradlew :docs:dokkaGenerate
       - name: Publish KDocs
         uses: peaceiris/actions-gh-pages@v3
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
-          publish_dir: ./build/dokka/htmlMultiModule
+          publish_dir: ./docs/build/dokka/html
           publish_branch: kdocs